The proposed experiments are designed to further our understanding of the formation and utilization of antibody structural diversity by the murine immune system towards creation of specificity for antigen and acquisition of a state of immunity. These experiments will directly address the following questions: 1) What fraction of antibody diversity is formed during the development of an immune response and how is such diversity created? 2) Does the immune system utilize available antibody diversity in fundamentally different ways depending on dose and type of antigen? 3) Do T lymphocytes? and 4) Do all members of the B cell population have an equal potential for creation of antibody diversity?